KANSAS CITY, Mo. (AP) — Mariano Rivera tore a ligament in his right knee before the New York Yankees lost 4-3 to the Kansas City Royals on Thursday night.

The 42-year-old right-hander was carted off the field after twisting his right knee shagging fly balls during batting practice.

Manager Joe Girardi revealed the severity of the injury after the game. Royals team doctor Vincent Key diagnosed a torn ACL after looking at the MRI.

“This is bad, there’s no question about it,” Girardi said.

Mike Moustakas matched a career high with three RBIs and made a defensive gem in the ninth for Kansas City Royals, backing a strong start by Danny Duffy (2-2). Jonathan Broxton was helped by two stellar defensive plays to finish for the save.

Baseball’s career saves leader was tracking down a ball hit by Jayson Nix in deep center field when his right knee appeared to buckle a step before the wall. He fell to the warning track and immediately grabbed his right knee, briefly covering his face with his glove and grimacing in pain.

Bullpen coach Mike Harkey was near Rivera when he went down, and he was the first to whistle for help. Girardi was watching batting practice from behind home plate and started running down, cutting across the outfield to get to his closer.

Near home plate, teammate Alex Rodriguez could be seen saying, “Oh, my God. Oh, my God.”

Harkey and Girardi helped to carry Rivera to the cart, gently setting him into the back with his knee propped up. The cart rounded the warning track before disappearing up a tunnel.

The remarkably durable reliever is in his 18th season. His last trip to the disabled list came in 2003, when he had a groin strain.

Rivera hasn’t shown any effects of age, either. He’s made at least 60 appearances each of the last nine seasons, setting a standard for bullpen excellence that may never be touched. He has five saves this season after blowing an opportunity on opening day.

Chipper Jones tore his Anterior Cruciate Ligament at 38. He returned to the big leagues about eight months later.

The 42-year-old Rivera regularly catches balls during batting practice as a way to keep in shape, and has jokingly said he’d like to play in the outfield before he retires.

“Mo shags every day. He’s been doing it the 20-something years I’ve known him,” Derek Jeter said. “It’s just a freak thing.”